Method and apparatus for debonding ceramic orthodontic brackets

ABSTRACT

An orthodontic bracket having mesial and distal sections is debonded from a tooth by pivoting the sections toward each other in respective arcs about a central reference axis extending in an occlusal-gingival direction. The mesial and distal sections are discrete and spaced apart from each other, or alternatively integrally joined by a relatively thin web that bends and optionally fractures upon debonding. A metallic archwire slot liner interconnects the mesial and distal sections and enhances sliding mechanics of the bracket. A pliers-like debonding tool includes jaws with stops for limiting the lingual depth of engagement of the laws with the mesial and distal sides of the bracket, to facilitate pivoting of the mesial and distal sections during debonding.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for removing a ceramicorthodontic bracket from a tooth.

2. Description of the Related Art

Orthodontic treatment involves movement of the teeth toward positionsfor correct occlusion. During treatment, tiny orthodontic appliancesknown as brackets are connected to the teeth, and an archwire is placedin a slot of each bracket. The archwire forms a track to guide movementof the teeth to orthodontically correct positions.

Orthodontic brackets are typically made of metal, ceramic or plastic.Metal brackets are widely used and are considered by many orthodontiststo have mechanical properties that are satisfactory for moving the teethto desired positions. Unfortunately, metal brackets are not aesthetic inthe mouth and often lead to comments of a "metallic mouth appearance"that can be an embarrassment to the patient.

Orthodontic brackets that are made of a plastic material are generallyconsidered more aesthetic than metal brackets. However, some plasticbrackets are stained by certain food and beverages and turn an unsightlycolor after a period of time. Moreover, the plastic material may slowlycreep in use such that the archwire slot widens and precise control oftooth movement is hindered.

Orthodontic brackets that are made of transparent or translucent ceramicmaterials overcome many of the problems associated with plasticbrackets, since ceramic material is resistant to staining and does notdeform by creep as in the case with plastic brackets. U.S. Pat. No.4,954,080, assigned to the assignee of the present invention, describesa color-free ceramic bracket made of polycrystalline material with atranslucency that permits the natural color of the tooth to diffuselyshow through the bracket. An improved translucent polycrystallineceramic bracket having a metallic archwire slot liner to enhance slidingmovement of the bracket on the archwire is described in pending U.S.application Ser. Nos. 08/061,215 and 08/061,164, both of which werefiled on May 13, 1993.

In the past, orthodontic brackets were commonly secured to bands thatwere placed around the teeth. Today, orthodontic brackets are oftenbonded directly to the surface of the teeth. Once treatment has beencompleted, the archwire is removed from the slot of the brackets andeach bracket is then removed from the associated tooth.

Metal brackets are typically debonded by using a peeling or pryingmotion. U.S. Pat. Nos. 3,986,265 and 4,248,587 describe plier-type handinstruments that are used with a prying action to remove orthodonticbrackets. U.S. Pat. No. 4,553,932, assigned to the assignee of thepresent invention, describes an peeling-type debonding tool having apull wire with a loop for hooking a wing of the bracket and applying apulling force to a tiewing located on one side of the bracket while apair of spaced apart abutments engage the tooth on opposite sides of thebracket.

Peeling-type debonding methods are usually considered satisfactory fordetaching brackets made of ductile materials such as metal. Debonding ofsuch brackets often begins by fracturing the adhesive bond along oneside of the bracket base, and then peeling or bending the base of thebracket so that the fracture propagates to remaining regions of theadhesive bond. In this manner, the debonding force is applied only to arelatively small, generally linear area at any particular point in time.

However, ceramic orthodontic brackets are relatively hard and brittle,and do not bend or flex like metal brackets during debonding. As aresult, debonding occurs by fracturing the adhesive bond in all areas atessentially the same time, rather than in a propagating type of fractureas occurs when metal brackets are debonded by a peeling-type motion.Pulling on the tiewings of a ceramic bracket is not normally recommendedbecause the ceramic material is brittle and the tiewings may break fromremaining portions of the bracket.

Damage to the tooth structure may result during a debonding operationwhen excessive stress is applied to the tooth during attempts to lift orpry the bracket from the tooth. Tooth damage is more likely to occurwhen the tooth structure is weakened or has been previously damaged;however, such weakened or previously damaged tooth structure oftencannot be noted by visual observation. Consequently, it is desirablethat brackets are removed from the teeth with as little force aspossible to minimize the risk of damage to the tooth.

It has been proposed in the past to weaken the strength of the bondbetween a ceramic bracket and the tooth so that debonding of the bracketis facilitated. However, such a solution is not entirely satisfactorybecause of the resulting increased likelihood that the bracket mayunintentionally, prematurely debond during treatment. For example, arelatively weak adhesive may not have sufficient strength to resistdebonding the bracket when the bracket is subjected to relatively largeforces, as when the patient bites into a relatively hard food object. Inother instances, a bracket may debond from forces exerted by thearchwire or orthodontic auxiliaries or attachments coupled to thebracket. Premature debonding of orthodontic brackets represents anuisance to both the orthodontist and the patient that is best avoided,since the detached bracket is normally re-bonded or replaced with a newbracket to finish treatment.

There is a need in the art for a ceramic bracket that provides theaesthetic advantages of ceramic material and functions similar to ametal bracket insofar as sliding mechanics are concerned, and yet isrelatively easy to debond from the tooth surface. There is also a needin the art for a new method of debonding ceramic orthodontic brackets,and a hand instrument that facilitates debonding of such brackets.

SUMMARY OF THE INVENTION

The present invention concerns a method of debonding a ceramicorthodontic bracket from a tooth that comprises the step of engagingmesial and distal sides of the bracket in areas located buccolabially ofa base of the bracket. The method also includes the step of urging theengaged mesial and distal sides toward each other in order to pivot atleast one of a mesial section and a distal section of the bracket awayfrom underlying areas of the tooth and about an axis generally parallelto a longitudinal axis of a channel that extends in a generallyocclusal-gingival direction between the mesial and distal sections ofthe bracket.

Another aspect of the invention is directed toward orthodontic apparatusthat comprises an orthodontic bracket having a mesial section with amesial side, a distal section with a distal side and an archwire slotextending in a generally mesial-distal direction. The bracket includes achannel that extends in a generally occlusal-gingival direction betweenthe mesial section and the distal section. The apparatus also includes adebonding tool having a pair of opposed jaws, a pair of handles eachconnected to one of the jaws and a coupling for connecting the handlesto each other. The coupling enables movement of the jaws toward eachother as the handles are moved toward each other. Each of the jawsincludes a wall for engaging one of the sides of the bracket. Each ofthe jaws includes a stop for limiting the depth in a lingual directionof engagement of the respective wall with the side of the bracket.

The present invention is also directed to an orthodontic bracketdebonding tool for debonding an orthodontic bracket having a labialside, a mesial section with a mesial side, a distal section with adistal side, and a slot extending in a generally mesial-distal directionin the mesial section and the distal section for receiving an archwire.The tool comprises a pair of opposed jaws and a pair of handles, eachhandle being connected to one of the jaws. A coupling movably connectsthe handles to each other and enables movement of the jaws toward eachother as the handles are moved toward each other. The jaws each includean outer end portion having a wall for engaging mesial or distal sidesof the bracket, a stop for engaging a labial side of the bracket and agroove extending through the wall for straddling an archwire received ina slot of the bracket.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view looking toward a labial side of anorthodontic bracket made in accordance with one embodiment of theinvention;

FIG. 2 is an elevational view of the bracket shown in FIG. 1, lookingtoward a mesial side of the bracket;

FIG. 3 is a bottom view of the bracket shown in FIGS. 1-2, lookingtoward a gingival side of the bracket and showing, for illustrativepurposes, the surface of a tooth upon which the bracket is mounted;

FIG. 4 is a view somewhat similar to FIG. 3 except that mesial anddistal sections of the bracket have been pivoted toward one another inorder to debond the bracket from the tooth;

FIG. 5 is a bottom view looking toward a gingival side of a ceramicorthodontic bracket according to another embodiment of the invention;

FIG. 6 is a view somewhat similar to FIG. 5 but in accordance withanother embodiment of the invention;

FIG. 7 is an elevational view of an orthodontic bracket according toanother embodiment of the invention, looking toward a labial side of thebracket;

FIG. 8 is a bottom view looking toward a gingival side of the bracketshown in FIG. 7;

FIG. 9 is an elevational view of the bracket depicted in FIGS. 7-8,looking toward a mesial side of the bracket;

FIG. 10 is a view somewhat similar to FIG. 8, but in accordance withanother embodiment of the invention;

FIG. 11 is a view somewhat similar to FIG. 7, but according to yetanother embodiment of the invention;

FIG. 12 is a bottom view looking toward a gingival side of the bracketshown in FIG. 11;

FIG. 13 is an exploded elevational view looking toward a labial side ofa bracket according to another embodiment of the invention;

FIG. 14 is a bottom exploded view looking toward a gingival side of thebracket shown in FIG. 13;

FIG. 15 is an elevational view looking toward a labial side of a bracketin accordance with another embodiment of the invention;

FIG. 16 is a bottom view looking toward a gingival side of the bracketof FIG. 15 along with a tooth upon which the bracket is bonded;

FIG. 17 is a perspective view of an orthodontic bracket debonding toolaccording to the invention; and

FIG. 18 is an inverted, enlarged, perspective, fragmentary view of oneend of the tool shown in FIG. 17 along with an orthodontic bracket andan archwire received in a slot of the bracket, showing jaws of the toolbeing moved toward positions of engagement with the bracket fordebonding the bracket from a tooth.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to FIGS. 1-3, a ceramic orthodontic bracket 20according to one embodiment of the invention is illustrated and includesa mesial (i.e., facing toward the middle of the dental arch) section 22and a distal (i.e., facing away from the middle of the dental arch)section 24. The mesial and distal sections 22, 24 each include anocclusal (i.e., toward the outer tip of the tooth) tiewing 26 and agingival (i.e., adjacent the gingiva or gum) tiewing 28 that extend overligature-receiving undercuts or grooves of the bracket 20.

An archwire slot 30 extends in a generally mesial-distal direction inthe mesial section 22 and the distal section 24, and preferably hasspaced apart, parallel occlusal and gingival walls interconnected by aperpendicular bottom wall and positioned to matingly receive an archwirehaving a rectangular cross-section for treatment according to theorthodontic technique known as the edgewise technique.

The bracket 20 includes a channel 32 that extends in a generallyocclusal-gingival direction between the mesial section 22 and the distalsection 24. As can be observed by comparing FIG. 3 with FIG. 2, thechannel 32 has a depth in a lingual (i.e., toward the tongue) directionthat is greater than the lingual depth of the archwire slot 30. Thechannel 32 in this embodiment has a rectangular configuration intransverse cross-section and extends from the occlusal side to thegingival side of the bracket 20.

The mesial section 22 includes a base having an external lingual surfacefor bonding the bracket 20 to a tooth. Likewise, the distal section 24has a base with an external lingual surface 36 for bonding the bracket20 to a tooth.

The base of the mesial section 22 and the base of the distal section 24are integrally connected by a thin, frangible web 38 that extendsdirectly beneath and along the entire length of the debonding channel32. Optionally, the channel 32 has a rounded bottom to enhancefracturing of the web 38 along the central, longitudinal axis of thechannel 32. As can be observed by reference to FIG. 3, an externallingual surface of the web 38 smoothly interconnects the bondingsurfaces 34, 36 of the mesial and distal sections 22, 24, and the threesurfaces together present a concave, compoundly curved configurationthat matches the convexly curved shape of a surface of a tooth 40 towhich the bracket 20 is adhesively bonded.

When the orthodontist desires to remove the bracket 20 from the tooth 40(FIGS. 3 and 4), a pliers-type tool, and preferably the debonding tooldescribed herein below, is used to fracture the adhesive bond betweenthe bracket 20 and the tooth 40. To this end, one jaw of the pliers-likedebonding tool is placed in a position to engage a mesial side 42 of themesial section 22 next to the occlusal tiewing 26 and the gingivaltiewing 28, while the remaining jaw is placed to engage a distal side 44of the distal section 22 in areas adjacent the occlusal tiewing 26 andthe gingival tiewing 28. The jaws engage the sides 42, 44 in buccolabial(i.e., toward the cheeks or lips) areas of the sections 22, 24, andpreferably do not engage those portions of the sections 22, 24 that arelocated lingually of the bottom of the debonding channel 32.

Next, the engaged mesial and distal sides 42, 44 are urged toward eachother in such a manner that one or both of the sections 22, 24 pivot indirection(s) toward each other in an arc and about a reference axis thatis generally parallel to the longitudinal, occlusal-gingival axis of thedebonding channel 32. As one or both of the sections 22, 24 pivot fromthe orientations as shown in FIG. 3 and toward the orientations as shownin FIG. 4, the web 38 fractures in the manner illustrated in FIG. 4,thereby enabling the bonding surfaces 34, 36 to detach from underlyingareas of the tooth 40.

The channel 32 greatly facilitates debonding of the bracket 20 from thetooth 40 because the pivotal or rocking motion is believed toconcentrate the debonding stresses in an effective manner along outer,mesial and distal edges of the bracket base. It is believed that suchstresses are significantly lower than the stresses that are needed todebond, for example, a ceramic bracket of similar size using a tensileforce in directions perpendicularly away from the tooth surface. As aconsequence, the pivoting debonding motion should reduce the likelihoodof injury to the enamel surface of the underlying tooth 40.

The bracket 20 is preferably made of a translucent, polycrystallineceramic material exhibiting light transmittance sufficient for thebracket 20 to assume the color of the underlying tooth. Suitable ceramicmaterials are described in U.S. Pat. No. 4,954,080, the disclosure ofwhich is incorporated by reference herein. Other ceramics may also beused, such as monocrystalline alpha-alumina, porcelain, glass,glass-ceramics and the like.

The buccolabial thickness of the web 38 is preferably less than about0.030 in. (0.7 mm) and preferably is about 0.015 in. (0.4 mm). Themesiodistal width of the channel 32 may be a relatively small dimension,such as 0.001 inc. (0.02 mm), that is sufficient to enable the mesialand distal sections 22, 24 to rock in an arc sufficient to debond fromthe tooth. Alternatively, the mesiodistal width of the debonding channel32 is of a larger dimension, such as 0.07 in. (1.8 mm), that issufficient to enable the channel 32 to receive a conventional ligaturewhen tied only about one of the sections 22, 24 for tooth rotation, andthereby enable the bracket 20 to function as a twin bracket.

Preferably, the mesiodistal width of the channel 32 is about 0.02 in.(0.5 mm), which is sufficient for the channel 32 to receive auxilliaryappliances while the bracket 20 is bonded to a tooth. Such constructionalso enables the bracket 20 to function as a twin bracket, whilemaintaining sufficient tiewing width for satisfactory tiewing strength.

Optionally, the debonding channel 32 is filled with a compliant materialsuch as a flexible plastic material in all areas except where thearchwire passes through the debonding channel 32. Such construction isan advantage in those instances where the orthodontist does not desireto use the bracket 20 as a twin bracket and wishes to avoid unneededrecesses or cavities in the bracket that might otherwise trap food orbacteria. The compliant material is sufficiently compressible to enablethe mesial and distal sections 22, 24 to be rocked toward each otherwithout undue hindrance during debonding.

A bracket 20a illustrated in FIG. 5 is another embodiment of theinvention that is somewhat similar to the embodiment illustrated inFIGS. 1-4. Unless otherwise mentioned, the elements in FIG. 5 bearingnumbers similar to the numbers in FIGS. 1-4 are the same as the elementsin FIGS. 1-4 and as a result a detailed description of such elementsshall not be repeated. However, and as can be appreciated by viewingFIG. 5, the bracket 20a has a debonding channel 32a with a differentconfiguration than the debonding channel 32 described in connection withFIGS. 1-4.

More particularly, the debonding channel 32a in FIG. 5 has opposed wallsthat are inclined toward each other as the labial side of the bracket20a is approached. The walls of the channel 32a include stop portions33a near the labial side of the bracket 20a that face each other. As canbe observed, the distance in FIG. 5 between the stop portions 33a issmaller than the mesial-distal width of the bottom of the channel 32a.

As the mesial side 22a and the distal side 24a are pivoted toward eachother to debond the bracket 20a from the surface of the tooth, the web38a bends slightly and the stop portions 33a come into contact with eachother. The initial, relatively small distance between the stop portions33a is sufficiently large to enable the web 38a to flex for debondingthe bracket 20, but is small enough to preclude the web 38a from bendingto such a degree that the web 38a fractures. Such construction increasesthe likelihood that the bracket 20a remains as a one-piece assemblyduring the debonding operation, and thereby reduces the likelihood thatone of the sections 22a, 24a will unintentionally fall in the mouth andbe aspirated or swallowed.

The embodiment of the invention that is illustrated in FIG. 6 concerns abracket 20b that is somewhat similar to the bracket 20 illustrated inFIGS. 1-4. Unless otherwise mentioned, elements of the bracket 20bbearing numerals corresponding to the numbered elements of FIGS. 1-4 aresimilar and consequently will not be described again in detail.

In FIG. 6, however, the web 38b includes a recess 39b that extends fromthe occlusal side to the gingival side of the bracket 20b directly belowthe bottom of the debonding channel 32b. The recess 39b has a V-shapedbottom surface that extends in a buccolabial direction away fromadjacent regions of the bonding surfaces 34b, 36b of the mesial section22 and the distal section 24b. The recess 39b thus interrupts thecontinuity of the smoothly curved, convex shape of the adjacent bondingsurfaces 34b, 36b and reduces the labial-lingual depth of the web 38b atits narrowest section in contrast to the embodiments shown in FIGS. 1-5.When the bracket 20b is debonded, the recess 39b facilitatesconcentration of stresses along the longitudinal, central axis of theweb 38b, such that in all likelihood the bracket 20b will fracture alongthe narrowest section of the web 38b while other portions of the bracket20b do not fracture and instead remain intact.

In the embodiment shown in FIGS. 7-9, a bracket 20c is again somewhatsimilar to the bracket 20 described in connection with FIGS. 1-4, andthe numerals in FIGS. 7-9 refer to elements that are substantiallyidentical to the elements bearing corresponding numerals in FIGS. 1-4except as explained in the paragraphs that follow.

The bracket 20c includes an elongated, one-piece metallic archwire slotliner 48c that extends across the mesial section 22c and the distalsection 24c. As illustrated in FIG. 9, the liner 48c has a rectangularconfiguration in transverse cross-section to receive a rectangulararchwire in mating relation. The mesial section 22c and the distalsection 24c each have a mesiodistally extending slot of sufficientdimensions to receive the archwire slot liner 48c.

Preferably, the archwire slot liner 48c is made of type 303 stainlesssteel having a thickness of 0.002 in. (0.05 mm). Preferably, thearchwire slot liner 48c is brazed to the mesial and distal sections 22c,24c and the difference in the thermal coefficients of expansion enablethe liner 48c to impose compressive forces on the sections 22c, 24c whenthe bracket 20c is cooled after the brazing operation. Additionaldetails regarding the brazing process and other information regardingthe archwire slot liner 48c, as well as other embodiments of thearchwire slot liner 48c, are set out in pending U.S. patent applicationsSer. Nos. 08/061,164 and 08/061,215.

When the bracket 20c is debonded from a tooth by urging the mesial anddistal sections 22c, 24c toward each other, the archwire slot linerbuckles to a somewhat crushed shape in areas of the debonding channel32c. Advantageously, the archwire slot liner 48c is securely fixed tothe mesial and distal sections 22c, 24c, and thus retains the sections22c, 24c together during and after a debonding operation to facilitateremoving the bracket 20c from the mouth in one piece. The archwire slotliner 48c also enhances sliding motion of the bracket 20c along thearchwire.

A bracket 20d as shown in FIG. 10 is somewhat similar to the bracket 20cshown in FIGS. 7-9, except that a mesial section 22d and a distalsection 24d are made as discrete units and are not integrally connectedtogether. The bracket 20d does not have a single web that integrallyinterconnects the sections 22d, 24d in a manner similar to the web 38c,but instead has a two-part web 38d that includes an elongated tab 52dthat is integrally connected to the base of the distal section 24d, anda groove 54d that is integrally connected to the base of the mesialsection 22d. The tab 52d and the groove 54d provide registrationstructure that facilitates retaining the mesial and distal sections 22d,24d together in a proper, abutting orientation before and duringorthodontic treatment.

The tab 52d and the groove 54d have mating convex and concaveconfigurations respectively, and extend the entire occlusal-gingivaldistance of the bracket 20d below the debonding channel 32d. Optionally,a thin layer of adhesive is applied to the interengaged surfaces of thetab 52d and the groove 54d to assist in retaining the mesial and distalsections 22d, 24d together during initial handling of the bracket 20dand during such time that the bracket 20d is used in therapy. Theadhesive bond, however, is sufficiently weak to provide a fracture pathfor the web 38d that is parallel to the longitudinal axis of the channel32d when debonding the bracket 20d. A suitable adhesive bond is made byapplying a glass frit to the tab 52d and the groove 54d before assembly,and then firing the assembled sections 22d, 24d to melt the glass andthereby bond the sections 22d, 24d together.

FIGS. 11 and 12 illustrate a bracket 20e according to another embodimentof the invention that is somewhat similar to the bracket 20d shown inFIG. 10. However, the bracket 20e as shown in FIGS. 11 and 12 havemesial and distal sections 22e, 24e that are spaced apart from eachother and interconnected with one another only by the archwire slotliner 48e. As such, the debonding channel 32e extends from the labialside of the bracket 20e to the bonding surfaces 34e, 36e.

The embodiments illustrated in FIG. 10 and FIGS. 11-12 provide amanufacturing advantage, especially when a dry pressing technique isutilized to make the brackets 20d, 20e. The mesial sections 22d, 22e andthe distal sections 24d, 24e may be separately pressed in directionsalong a mesial-distal axis rather than along a labial-lingual axis as iscommonly used when dry pressing conventional, one-piece ceramicbrackets. By pressing the sections separately, relatively complex designfeatures, such as slots to receive the archwire slot liner and grooved,undercut regions below the tiewings can be pressed in the green parts,rather than being machined in a secondary operation. Optionally, grit orglass may be added to the base surfaces 34d-e, 36d-e to enhance bondingof the brackets 20d-e directly to a tooth.

Further, in some instances, the mesial section and the distal section inthe embodiments shown in FIGS. 10 and 11-12 may be identical, such thata single mold or die can be used to make both sections. In such aninstance, it is preferred to replace the compound curved bondingsurfaces of the mesial and distal sections with generically curvedsurfaces that are oriented to approximate the orientation of theunderlying tooth surface, and use an orthodontic adhesive withsufficient strength to overcome the resulting lack of a precise,matching configuration between the compound curve of the external toothsurface and the bracket base. Optionally, the slot liner may be curvedalong its length in the labial-lingual/mesial-distal plane to enhancethe fit between the tooth surface and the bracket base.

FIGS. 13-14 depict a bracket 20f according to another embodiment of theinvention. The bracket 20f has a mesial section 22f and a distal section24f that advantageously are identical and consequently reduce the costsof manufacture. Each self-mating section 22f, 24f includes amesiodistally extending peg 25f that is received in a mating hole 27f ofthe other section 22f, 24f. Optionally, an adhesive is used to retainthe pegs 25f in the holes 27f. As another alternative, bracket 20f mayinclude a metal archwire slot liner to enhance sliding mechanics andalso to assist in retaining the sections 22f, 24f together. Duringdebonding, the pegs 25f break as the sections 22f, 24f are rocked towardeach other about an occlusal-gingival debonding channel 32f.

FIGS. 15-16 illustrate a bracket 20g according to another embodiment ofthe invention. The bracket 20g is substantially similar to the bracket20 shown in FIGS. 1-4, but includes a pair of spaced-apart bridges 29gthat integrally interconnect mesial and distal sections 22g, 24g. Thebridges 29g are spaced buccolabially from frangible web 38g and enhancethe strength of the bracket 20g . However, bridges 29g are readilyremoved with a diamond burr prior to debonding: subsequently thesections 22g, 24g are pivoted toward each other about debonding channel32g. (In this regard, it should be understood that bridges similar tobridges 29g may be used with the other brackets described above.

An orthodontic debonding tool for debonding the brackets mentioned aboveis shown in FIGS. 17 and 18 and is designated by the numeral 60. Thetool 60 is shown for illustrative purposes in FIG. 18 as used inconnection with the bracket 20, but is also useful for debonding otherbrackets according to the invention such as brackets 20a-20e. Thedebonding tool 60 has a pliers-like configuration and includes a pair ofopposed jaws 62 as well as a pair of handles 64.

Each of the handles 64 is connected to a respective one of the jaws 62,and the handles 64 and the jaws 62 are essentially identical. Thehandles are coupled together by a pivot 66 that enables the jaws 62 tomove toward and away from each other as the handles 64 are moved towardor away from each other.

Each of the jaws 62 includes an outer end portion having a wall 68 forengaging either the mesial side 42 or the distal side 44 of the bracket20. Each jaw 62 also includes a wall 70 oriented perpendicular to thewall 68, for engaging the labial surface of the bracket 20, oralternatively the labial side of an archwire 72 that is received in thearchwire slot 30 of the bracket 20. A groove 74 extends through the wall68 for straddling the archwire 72 in the manner shown in FIG. 18.

The walls 70 function as a stop to limit the lingual depth of engagementof the walls 68 with the respective mesial and distal sides 42, 44 ofthe bracket 20. Thus, when the handles 64 are squeezed together to closethe jaws 62, the walls 68 apply compressive forces only to labialportions of the mesial and distal sections 22, 24 and not to baseportions of the bracket 20 in areas lingually of the bottom of thedebonding channel 32. Such construction facilitates rocking of themesial and distal sections 22, 24 about the web 38 and helps insure thatthe web 38 will fracture in a direction along the longitudinal axis ofthe channel 32. Consequently, the probability is increased that thebracket 20 will fracture into only two pieces (i.e., the mesial anddistal sections 22, 24) or, at most, three pieces (i.e., the sections22, 24 and the web 38). The recessed walls 68, 70 advantageously serveas a trap in some instances during debonding when the archwire 72 hasbeen removed, so that the broken pieces do not fall into the oralcavity.

Another advantage of the present invention is that a set of brackets 20can be debonded from corresponding teeth in one arch of the mouth whileall of such brackets 20 remain connected to the common archwire 72 byligatures (not shown in FIG. 18) that are conventionally used duringorthodontic treatment. The groove 74 enables the jaws 62 to be placedover the archwire 72 as well as the bracket 20 while enabling theligature to remain in place to couple the bracket 20 to the archwire 72.The orthodontist can debond each bracket 20 in turn, and then lift thearchwire 72 with all attached brackets 20 from the mouth. Such anadvantage is important because less time is needed for debonding, andthere is less likelihood that one or more of the brackets 20 will dropinto the oral cavity and become ingested or aspirated during thedebonding operation.

In the bracket 20 shown in FIG. 18, the archwire 72 is received in thearchwire slot 30 to such a lingual depth that the labial side of thearchwire 72 is located lingually of the labial side of the bracket 20.As such, the walls 70 engage the labial sides of the mesial and distalsections 22, 24 to limit the lingual engagement of the walls 68 with themesial and distal sides 42, 44. As an alternative, the wall 70 mayinclude a protruding portion for engaging the labial side of thearchwire 72, or alternatively the archwire slot 30 of the bracket 20 maybe located nearer the labial side of the bracket 20, so that engagementof the wall 70 with the archwire 72 serves to limit the depth of lingualengagement of the walls 68 on the mesial and distal sides 42, 44.

The debonding tool 60 is preferably made of a corrosion resistant 400series stainless steel, such as type 420, that is suitable for repeatedsterilization. As an alternative to the straight-line configuration ofthe tool 60 illustrated in FIGS. 17 and 18, the jaws may extend in adirection at an angle in the range of about 25 to 40 degrees relative tothe major extent of the handles, to facilitate access to brackets bondedto posterior teeth.

We claim:
 1. A method of debonding a ceramic orthodontic bracket from atooth comprising the steps of:engaging a mesial side and a distal sideof the bracket in areas located buccolabially of a base of the bracket;and urging the engaged mesial and distal sides toward each other inorder to pivot at least one of a mesial section and a distal section ofthe bracket away from underlying areas of the tooth and about areference axis generally parallel to a longitudinal axis of a channelthat extends in a generally occlusal-gingival direction between themesial section and the distal section of the bracket.
 2. The method ofclaim 1, wherein said step of urging the mesial side and the distal sidetoward each other includes the step of fracturing a frangible web of thebracket that extends in a direction generally parallel to thelongitudinal axis of the channel.
 3. The method of claim 2, wherein saidstep of fracturing a web includes the step of breaking an adhesive bondbetween structure interconnecting the mesial section and the distalsection in areas located lingually of the channel.
 4. The method ofclaim 2, wherein said step of fracturing a web includes the step offracturing a thin ceramic web that integrally interconnects the mesialsection and the distal section in areas of the bracket lingually of thechannel.
 5. The method of claim 1, wherein said step of urging themesial side and the distal side toward each other includes the step ofbuckling a metal liner that extends along an archwire slot of thebracket.
 6. The method of claim 1, wherein said step of urging theengaged mesial side and distal side toward each other includes the stepof compressing a compliant material located in the channel.
 7. Themethod of claim 1, wherein said step of urging the engaged mesial anddistal sides toward each other is carried out while an archwire is inengagement with the bracket.
 8. Orthodontic apparatus comprising:aceramic orthodontic bracket having a mesial section with a mesial side,a distal section with a distal side and an archwire slot extending in agenerally mesial-distal direction, said bracket including a channelextending in a generally occlusal-gingival direction between said mesialsection and said distal section; and a debonding tool having a pair ofopposed jaws, a pair of handles each connected to one of said jaws and acoupling for connecting said handles to each other, said couplingenabling movement of said jaws toward each other as said handles aremoved toward each other, each of said jaws including a wall for engagingone of said mesial and said distal sides of said bracket, each of saidjaws including a stop for limiting the depth in a lingual direction ofengagement of the respective wall with said mesial and said distal sideof said bracket.
 9. The apparatus of claim 8, wherein said bracketincludes a labial side, and wherein said stop engages said labial sideof said bracket.
 10. The apparatus of claim 8, wherein said stop engagesa labial side of an archwire when an archwire is received in saidarchwire slot of said bracket.
 11. The apparatus of claim 8, whereinsaid walls each include a groove for straddling an archwire received insaid archwire slot.
 12. The apparatus of claim 8, wherein each of saidjaws includes a recess, and wherein said wall is located in said recess.13. An orthodontic bracket debonding tool for debonding an orthodonticbracket having a labial side, a mesial section with a mesial side, adistal section with a distal side, and a slot extending in a generallymesial-distal direction in said mesial section and said distal sectionfor receiving an archwire, said tool comprising:a pair of opposed jaws;a pair of handles, each handle being connected to one said jaws; and acoupling movably connecting said handles to each other, said couplingenabling movement of said jaws toward each other as said handles aremoved toward each other, said jaws each including an outer end portionhaving a wall for engaging the mesial side and the distal siderespectively of the bracket, a stop for engaging the labial side of thebracket and a groove extending through the wall for straddling anarchwire received in the slot of the bracket.
 14. The hand tool of claim13, wherein said coupling comprises a pivot that enables said jaws tomove in an arc as said jaws move toward each other, and wherein saidwall of each of said jaws is located in a reference plane generallyperpendicular to said arc.
 15. The hand tool of claim 13, wherein eachof said jaws includes a recess, and wherein said wall of each of saidjaws is located in said recess.